8 ms·

Whats special about D? why should i learn it?

gmfawcett 10y ago
Except for perhaps Lisp languages, almost no language makes compile-time computing and code-generation so easy. This allows for some really powerful language features that can be designed as libraries, and puts this power in the hands of "regular developers" rather than only in the hands of template wizards.
- jordigh 10y ago
  Yeah, I really love that at compile time you can meta-program in almost the same language that you use for normal run-time things. I think the comparison to lisp is apt. It almost feels like lisp macros. Think C++ template metaprogramming but much, much easier and thus, seemingly more powerful. It's not that you couldn't do the same in C++, but D's metaprogramming is so much more accessible that it makes you want to use it.
  - dbcurtis 10y ago
    For someone who knows zero about D, but is a total Pythonista, how would you compare the meta-programming facilities?
    - jordigh 10y ago
      I guess the best comparison to Python would be the dunder methods. You know how in Python a class really is just a dict, right? Like, foo.bar is pretty much syntactic sugar for foo.__get_attribute__(foo.__dict__['bar']) in most cases. Or how a + b is sugar for a.__plus__(b). Well, imagine that all of the things you can do in Python by messing with dunder methods, function decorators, or metaclasses could be precomputed by a compiler and would not even execute at all during runtime. It makes everything really fast at runtime and easy to precompute at compile time.
      - dbcurtis 10y ago
        Well, overriding dunder methods isn't really metaprogramming. It's just method inheritance/override. Is there anything in D similar to decorators? How does the registration pattern work in D, for instance?
        gmfawcett 10y ago
        Do you mean like this kind of registration decorator? https://github.com/rejectedsoftware/vibe.d/blob/master/examples/rest/source/app.d#L232 https://github.com/rejectedsoftware/vibe.d/blob/master/examp... Decorators (in D, 'user defined attributes', or UDA) work differently. It's not a function-composition feature, but more of a tagging feature. You write a class, function, etc., tag it with custom attributes; and then have a separate compile-time function walk over your code, find the decorators, and augment the code based the meaning of the tags. (I used to wish that D had adopted Python-style decorators, since they are easy to reason about and implement, but I can see the logic of the more general UDA system that they adopted.) In practice, though, you would often use templates to achieve the same effect. Given a memoize template (really, just a memoize function), and an expensive-computation function, auto fastComputer = memoize!expensiveComputer; produces roughly the equivalent of @memoize def expensiveComputer(): ... but with opportunities for compile-time optimization.
      - gmfawcett 10y ago
        Yes, and plus you get type safety with all of that! When I'm writing in D, my editor marks all the type errors (and typos) in my code, almost as fast as I make them. The DMD compiler is so quick that there's almost no lag. This leads not only to a rapid development cycle, but a much higher level of reassurance (than I've had when writing, e.g., metaclass hacks in Python).
  - jacques_chirac 10y ago
    There's plenty you can do with D but not C++, see regex, bitfields, swap member-by-member with checks for mutual pointers, the pegged library for grammars, etc etc.
    - jordigh 10y ago
      I don't know, Boost has me convinced that even things like regexes in C++ templates could be possible, if your compiler has a big enough stack to handle very deep template recursions. It's theoretically possible to build a regex parser in C++ templates, right? It would be horrible, but possible.
      - humanrebar 10y ago
        > It's theoretically possible to build a regex parser in C++ templates, right? You'd probably do large portions of it in "constexpr" types and functions rather than relying on recursive metaprogramming techniques. They are also planning on adding overloading based on whether a function is constexpr, which is important if you want the same library to support both compile-time and run-time matchers. So it's all theoretically possible already. But D has the advantage here in that it's not just possible but usable.
      - qznc 10y ago
        With D it is possible and not horrible and already done. ;) Talk: http://dconf.org/2014/talks/olshansky.html http://dconf.org/2014/talks/olshansky.html
- dom96 10y ago
  Anybody out there that has experience with both Nim and D? I am curious how they both compare in terms of metaprogramming.
  - gmfawcett 10y ago
    I've dabbled with Nim. It's also a great language with great metaprogramming features. Plus a fast compiler that generates very lean code. (The real reason I stick with D over Nim, above all else, is RAII -- once you have it, it's really hard to live without. Okay, that, and also ranges, and array/string slices... they are fantastic to work with. Nim's got a better GC story right now, IMO, but there's a lot of activity in the D community to become more competitive in that space.) I found that some of the Nim's MP features, in particular AST macros, are a little harder to work with than D's templates and compile-time function evaluation. You get a lot of flexibility, but the cost is high. I'm not a big fan of how "mixin" is used in D to splice source-text into a generated function, it's certainly less principled than an AST transformation, but in practice the resulting code tends to be concise and easily read, whereas the AST-macro approach introduces a lot of accidental "noise" and complexity. The complexity raises the bar for reaching for a compile-time solution, where in D it seems equally as natural to write compile-time code as it does to write regular code. (Not to pick on a strawman, though -- AST macros are not Nim's only MP tool.) The Nim MP feature I never really played with was the rewrite rules. They seem interesting in theory, but maybe a little too magical for my liking! I have a lot of respect for Nim. I am glad we live in a world with so many options. Like Walter said in an earlier comment, it's an embarrassment of riches. :)
    - theprotocol 10y ago
      Thanks for the writeup. I've just been evaluating Rust, D, and Nim, and reading about your experience has been helpful. Can you elaborate on how D is planning to sort out the garbage collection? Nim's GC is extremely fast and thread local, and can be disabled without breaking libraries (according to the author, it does something with memory regions that I haven't 100% grasped yet). I've googled about D's garbage collector and it's apparently been discussed as the language's biggest flaw since 2013, but I can't find any information whatsoever on what's being done in that regard.
amelius 10y ago
Also, how does D compare to Rust? (If I'm going to learn a new system programming language, which one should I pick?)
- Keyframe 10y ago
  D2, as a language, favourably. As an ecosystem, not favourably. I REALLY ENJOYED D1, REALLY! (CAPS 11). D1 was like C, but better. It was heavenly. D2 is like C++, but better. Not my cup of tea though. Give it a spin for a day or two. I'm sure you'll like it if you like C++. Trouble arises, as with all niche languages, when you try to move to production and you have to source libraries and/or support.
- Rusky 10y ago
  D has been around longer, has powerful compile-time metaprogramming tools, and has a very fast compiler. However, it has a garbage collector, and is not entirely memory-safe by default (though is beginning to optionally incorporate some ideas from Rust [edit: or not], maybe making that easier once you put in the work). It seems to follow C or C++ in what sorts of things it makes language-level features. Rust is newer (though being used in some big projects like Firefox/Servo, Visual Studio Code's search functionality now uses it by default, etc), has (afaiu) a more powerful type system, and is entirely memory-safe by default. However, this makes it somewhat harder to learn at first, and it also has a relatively slow compiler. It follows ML-style languages a bit more, with things like pattern matching and sum types built into the language. Personally, I prefer Rust, because it feels like a stronger foundation with the ML-like type system and no GC. YMMV though, depending on what is important to you.
  - deleted 10y ago
    [deleted]
  - WalterBright 10y ago
    D's memory safe notions are very different from Rust's.
    - 10y ago
bachmeier 10y ago
If you want to work with C code, it is an excellent choice. I use it for numerical computing. It's an easy language to learn, no need to worry about memory management if you don't want/need to, generally good syntax, nice compile time features. Overall the best "better C" in my opinion.
- kaleidic 10y ago
  See bachmeier work on D to R integration.
grok2 10y ago
I think one of the very good features of D is that it provides a lot of infrastructure that helps with lots of little generic things -- things that are not really needed in the language, but help reduce the amount of code you write or simplify common actions you take. It seems like Walter (and all the other contributors) have distilled their experience writing programs into creating a language that helps a lot with some of these things. Stuff that I particularly like. Assert/Enforce: http://ddili.org/ders/d.en/assert.html http://ddili.org/ders/d.en/assert.html , Unit testing: http://ddili.org/ders/d.en/unit_testing.html http://ddili.org/ders/d.en/unit_testing.html , Contract programming help: http://ddili.org/ders/d.en/contracts.html http://ddili.org/ders/d.en/contracts.html, and http://ddili.org/ders/d.en/invariant.html http://ddili.org/ders/d.en/invariant.html , Scope (love this): http://ddili.org/ders/d.en/scope.html http://ddili.org/ders/d.en/scope.html And the other usuals -- templates, mixins, etc.... BTW, I mostly use D as a better C than as a better C++...
- vram22 10y ago
  Good list. Another good feature: Interfacing to C is somewhat easy at least for the basics. (I haven't looked at advanced cases yet, but maybe someone else can comment on that.) https://dlang.org/spec/interfaceToC.html https://dlang.org/spec/interfaceToC.html This is a great feature IMO, because it allows you to (re)use the huge number of existing C libraries out there. Here is a simple example: Calling a simple C function from D - strcmp: https://jugad2.blogspot.in/2016/09/calling-simple-c-function-from-d-strcmp.html https://jugad2.blogspot.in/2016/09/calling-simple-c-function... There's a handful more small examples of a few things D can easily do, here on my blog: https://jugad2.blogspot.in/search/label/DLang https://jugad2.blogspot.in/search/label/DLang (And of course, there are many more at the DLang tour site - https://tour.dlang.org/ https://tour.dlang.org/ ) Also, there are a few good videos about D (alone) and being discussed along with other languages, at my blog's DLang posts link above. I'll just put some post titles here to give a quick idea: Simple parallel processing in D with std.parallelism Using std.datetime.StopWatch to time sections of D code Read from CSV with D, write to PDF with Python Command line D utility - find files matching a pattern under a directory min_fgrep: minimal fgrep command in D num_cores: find number of cores in your PC's processor Func-y D + Python pipeline to generate PDF file_sizes utility in D: print sizes of all files under a directory tree deltildefiles: D language utility to recursively delete vim backup files [DLang]: A simple file download utility in D Getting CPU info with D (the D language)

Except for perhaps Lisp languages, almost no language makes compile-time computing and code-generation so easy. This allows for some really powerful language features that can be designed as libraries, and puts this power in the hands of "regular developers" rather than only in the hands of template wizards.

jordigh 10y ago
Yeah, I really love that at compile time you can meta-program in almost the same language that you use for normal run-time things. I think the comparison to lisp is apt. It almost feels like lisp macros. Think C++ template metaprogramming but much, much easier and thus, seemingly more powerful. It's not that you couldn't do the same in C++, but D's metaprogramming is so much more accessible that it makes you want to use it.
- dbcurtis 10y ago
  For someone who knows zero about D, but is a total Pythonista, how would you compare the meta-programming facilities?
  - jordigh 10y ago
    I guess the best comparison to Python would be the dunder methods. You know how in Python a class really is just a dict, right? Like, foo.bar is pretty much syntactic sugar for foo.__get_attribute__(foo.__dict__['bar']) in most cases. Or how a + b is sugar for a.__plus__(b). Well, imagine that all of the things you can do in Python by messing with dunder methods, function decorators, or metaclasses could be precomputed by a compiler and would not even execute at all during runtime. It makes everything really fast at runtime and easy to precompute at compile time.
    - dbcurtis 10y ago
      Well, overriding dunder methods isn't really metaprogramming. It's just method inheritance/override. Is there anything in D similar to decorators? How does the registration pattern work in D, for instance?
      - gmfawcett 10y ago
        Do you mean like this kind of registration decorator? https://github.com/rejectedsoftware/vibe.d/blob/master/examples/rest/source/app.d#L232 https://github.com/rejectedsoftware/vibe.d/blob/master/examp... Decorators (in D, 'user defined attributes', or UDA) work differently. It's not a function-composition feature, but more of a tagging feature. You write a class, function, etc., tag it with custom attributes; and then have a separate compile-time function walk over your code, find the decorators, and augment the code based the meaning of the tags. (I used to wish that D had adopted Python-style decorators, since they are easy to reason about and implement, but I can see the logic of the more general UDA system that they adopted.) In practice, though, you would often use templates to achieve the same effect. Given a memoize template (really, just a memoize function), and an expensive-computation function, auto fastComputer = memoize!expensiveComputer; produces roughly the equivalent of @memoize def expensiveComputer(): ... but with opportunities for compile-time optimization.
    - gmfawcett 10y ago
      Yes, and plus you get type safety with all of that! When I'm writing in D, my editor marks all the type errors (and typos) in my code, almost as fast as I make them. The DMD compiler is so quick that there's almost no lag. This leads not only to a rapid development cycle, but a much higher level of reassurance (than I've had when writing, e.g., metaclass hacks in Python).
- jacques_chirac 10y ago
  There's plenty you can do with D but not C++, see regex, bitfields, swap member-by-member with checks for mutual pointers, the pegged library for grammars, etc etc.
  - jordigh 10y ago
    I don't know, Boost has me convinced that even things like regexes in C++ templates could be possible, if your compiler has a big enough stack to handle very deep template recursions. It's theoretically possible to build a regex parser in C++ templates, right? It would be horrible, but possible.
    - humanrebar 10y ago
      > It's theoretically possible to build a regex parser in C++ templates, right? You'd probably do large portions of it in "constexpr" types and functions rather than relying on recursive metaprogramming techniques. They are also planning on adding overloading based on whether a function is constexpr, which is important if you want the same library to support both compile-time and run-time matchers. So it's all theoretically possible already. But D has the advantage here in that it's not just possible but usable.
    - qznc 10y ago
      With D it is possible and not horrible and already done. ;) Talk: http://dconf.org/2014/talks/olshansky.html http://dconf.org/2014/talks/olshansky.html
dom96 10y ago
Anybody out there that has experience with both Nim and D? I am curious how they both compare in terms of metaprogramming.
- gmfawcett 10y ago
  I've dabbled with Nim. It's also a great language with great metaprogramming features. Plus a fast compiler that generates very lean code. (The real reason I stick with D over Nim, above all else, is RAII -- once you have it, it's really hard to live without. Okay, that, and also ranges, and array/string slices... they are fantastic to work with. Nim's got a better GC story right now, IMO, but there's a lot of activity in the D community to become more competitive in that space.) I found that some of the Nim's MP features, in particular AST macros, are a little harder to work with than D's templates and compile-time function evaluation. You get a lot of flexibility, but the cost is high. I'm not a big fan of how "mixin" is used in D to splice source-text into a generated function, it's certainly less principled than an AST transformation, but in practice the resulting code tends to be concise and easily read, whereas the AST-macro approach introduces a lot of accidental "noise" and complexity. The complexity raises the bar for reaching for a compile-time solution, where in D it seems equally as natural to write compile-time code as it does to write regular code. (Not to pick on a strawman, though -- AST macros are not Nim's only MP tool.) The Nim MP feature I never really played with was the rewrite rules. They seem interesting in theory, but maybe a little too magical for my liking! I have a lot of respect for Nim. I am glad we live in a world with so many options. Like Walter said in an earlier comment, it's an embarrassment of riches. :)
  - theprotocol 10y ago
    Thanks for the writeup. I've just been evaluating Rust, D, and Nim, and reading about your experience has been helpful. Can you elaborate on how D is planning to sort out the garbage collection? Nim's GC is extremely fast and thread local, and can be disabled without breaking libraries (according to the author, it does something with memory regions that I haven't 100% grasped yet). I've googled about D's garbage collector and it's apparently been discussed as the language's biggest flaw since 2013, but I can't find any information whatsoever on what's being done in that regard.

amelius 10y ago

Also, how does D compare to Rust? (If I'm going to learn a new system programming language, which one should I pick?)

Keyframe 10y ago
D2, as a language, favourably. As an ecosystem, not favourably. I REALLY ENJOYED D1, REALLY! (CAPS 11). D1 was like C, but better. It was heavenly. D2 is like C++, but better. Not my cup of tea though. Give it a spin for a day or two. I'm sure you'll like it if you like C++. Trouble arises, as with all niche languages, when you try to move to production and you have to source libraries and/or support.
Rusky 10y ago
D has been around longer, has powerful compile-time metaprogramming tools, and has a very fast compiler. However, it has a garbage collector, and is not entirely memory-safe by default (though is beginning to optionally incorporate some ideas from Rust [edit: or not], maybe making that easier once you put in the work). It seems to follow C or C++ in what sorts of things it makes language-level features. Rust is newer (though being used in some big projects like Firefox/Servo, Visual Studio Code's search functionality now uses it by default, etc), has (afaiu) a more powerful type system, and is entirely memory-safe by default. However, this makes it somewhat harder to learn at first, and it also has a relatively slow compiler. It follows ML-style languages a bit more, with things like pattern matching and sum types built into the language. Personally, I prefer Rust, because it feels like a stronger foundation with the ML-like type system and no GC. YMMV though, depending on what is important to you.
- deleted 10y ago
  [deleted]
- WalterBright 10y ago
  D's memory safe notions are very different from Rust's.
  - 10y ago

bachmeier 10y ago

If you want to work with C code, it is an excellent choice. I use it for numerical computing. It's an easy language to learn, no need to worry about memory management if you don't want/need to, generally good syntax, nice compile time features. Overall the best "better C" in my opinion.

kaleidic 10y ago
See bachmeier work on D to R integration.

grok2 10y ago

I think one of the very good features of D is that it provides a lot of infrastructure that helps with lots of little generic things -- things that are not really needed in the language, but help reduce the amount of code you write or simplify common actions you take. It seems like Walter (and all the other contributors) have distilled their experience writing programs into creating a language that helps a lot with some of these things. Stuff that I particularly like. Assert/Enforce: http://ddili.org/ders/d.en/assert.html http://ddili.org/ders/d.en/assert.html , Unit testing: http://ddili.org/ders/d.en/unit_testing.html http://ddili.org/ders/d.en/unit_testing.html , Contract programming help: http://ddili.org/ders/d.en/contracts.html http://ddili.org/ders/d.en/contracts.html, and http://ddili.org/ders/d.en/invariant.html http://ddili.org/ders/d.en/invariant.html , Scope (love this): http://ddili.org/ders/d.en/scope.html http://ddili.org/ders/d.en/scope.html And the other usuals -- templates, mixins, etc.... BTW, I mostly use D as a better C than as a better C++...

vram22 10y ago
Good list. Another good feature: Interfacing to C is somewhat easy at least for the basics. (I haven't looked at advanced cases yet, but maybe someone else can comment on that.) https://dlang.org/spec/interfaceToC.html https://dlang.org/spec/interfaceToC.html This is a great feature IMO, because it allows you to (re)use the huge number of existing C libraries out there. Here is a simple example: Calling a simple C function from D - strcmp: https://jugad2.blogspot.in/2016/09/calling-simple-c-function-from-d-strcmp.html https://jugad2.blogspot.in/2016/09/calling-simple-c-function... There's a handful more small examples of a few things D can easily do, here on my blog: https://jugad2.blogspot.in/search/label/DLang https://jugad2.blogspot.in/search/label/DLang (And of course, there are many more at the DLang tour site - https://tour.dlang.org/ https://tour.dlang.org/ ) Also, there are a few good videos about D (alone) and being discussed along with other languages, at my blog's DLang posts link above. I'll just put some post titles here to give a quick idea: Simple parallel processing in D with std.parallelism Using std.datetime.StopWatch to time sections of D code Read from CSV with D, write to PDF with Python Command line D utility - find files matching a pattern under a directory min_fgrep: minimal fgrep command in D num_cores: find number of cores in your PC's processor Func-y D + Python pipeline to generate PDF file_sizes utility in D: print sizes of all files under a directory tree deltildefiles: D language utility to recursively delete vim backup files [DLang]: A simple file download utility in D Getting CPU info with D (the D language)